Right now there HasOne and HABTM (Has and Belongs To Many) relationships are implemented. You could create a reflexive relationship simply by adding a HasOne field that points to the same class in which it belongs.

i.e.

class Person
{
PrimaryKey id;
HasOne!(Person) parent;
}

As of now, I have not planned on any specific built-in support for referential integrity. What would you suggest?